1. Field of the Invention
The present invention relates to polymers and to methods of making polymers. In another aspect, the present invention relates to polycarbonate prepolymer, to methods of making such prepolymer, to polycarbonate polymer, and to methods of making such polycarbonate polymer. In even another aspect, the present invention relates to a crystallized polycarbonate prepolymer, to methods of crystallizing polycarbonate prepolymer utilizing a diluent and solvent mixture, utilizing heat with shear generation, or utilizing seeding, to a method making polycarbonate by solid state polymerization, and to polycarbonate made therefrom.
2. Description of the Related Art
Over the last few years, aromatic polycarbonates have found utility in various applications requiring engineering plastics with outstanding heat resistance, impact resistance, and transparency. Due to the popularity of aromatic polycarbonates, much prior art exists with respect to production processes for such aromatic polycarbonates.
The phosgene method
A well known commercially utilized production process is the so-called "phosgene method" involving an interfacial polycondensation process between an aromatic dihydroxy compound such as 2,2-bis(4-hydroxyphenyl) propane (henceforth referred to as bis-phenol A) and phosgene. In the phosgene method, a solvent mixture consisting of water or an aqueous alkali solution and an organic solvent which is not miscible with water is normally used. Commercially, a mixed solvent of aqueous sodium hydroxide and methylene chloride is used. A tertiary amine or a quaternary ammonium compound is used as a polymerization catalyst. The hydrogen chloride formed as a side product is removed in the form of a salt with a base. The weight average molecular weight of the aromatic polycarbonate formed is generally 15,000-70,000 and normally is 16000-40,000.
Unfortunately, the interfacial polycondensation "phosgene process" suffers from many disadvantages as are well known in the literature, examples of which are listed in U.S. Pat. No. 5,204,377.
Transesterification (or-melt) process
Various prior art "transesterification" (also known as "melt") processes are known in which an aromatic polycarbonate is formed from an aromatic dihydroxy compound and diaryl carbonate. As commercially practiced, a polycarbonate is obtained by an ester exchange reaction between bis-phenol A and diphenyl carbonate conducted in a molten state in the presence of a catalyst to release the phenol to produce a polycarbonate. However, in this method, the degree of polymerization of the desired aromatic polycarbonate can not be increased unless phenol and finally diphenyl carbonate are removed by distillation from a highly viscous (8,000-20,000 poise at 280.degree. C.) molten material of the polycarbonate formed.
Unfortunately, the transesterification process also suffers from many disadvantages as are well known in the literature, examples of which are listed in U.S. Pat. No. 5,204,377.
Solid-slate condensation polymerization
Solid-state condensation polymerization has developed as an alternative to the phosgene process and the transesterification process for making polycarbonate.
In solid-state condensation polymerization, a high molecular weight polycarbonate is produced by first preparing a relatively low molecular weight crystallized polycarbonate prepolymer followed by subsequent solid-state polymerization of the crystallized prepolymer.
In general, a solid phase polymerization process is made possible by an ability of a polymer to sustain a solid phase state at temperatures above the glass transition temperature without causing the polymer to fuse (when the temperature for the polymerization is below the glass transition temperature, the polymerization does not take place since the molecular movement is inhibited).
As disclosed in International Patent Application No. PCT/JP88/989, solid-state condensation polymerization could be effectively performed to increase the molecular weight of formed polycarbonate in the production of aromatic polycarbonate from, as starting materials, dihydroxydiaryl alkane, such as bisphenol A, and a diaryl carbonate, such as diphenyl carbonate. As disclosed in PCT/JP88/989, a high quality aromatic polycarbonate in which a substantially amorphous prepolymer having hydroxyl and aryl carbonate groups as terminal groups is crystallized and then subjected to solid-state condensation polymerization.
U.S. Pat. No. 5,266,659, issued Nov. 30, 1993, discloses a solid state process for the preparation of high molecular weight poly(arylcarbonates) from amorphous oligomer. Specifically, the process involves heating in a controlled manner, a BPA-carbonate oligomer in the presence of a catalyst selected from alkali metal aryl acid, alkali metal borohydrial and a quarternary ammonium salt of bioxyanion derived from a carboxylic acid poly(arylcarbonate)s of high molecular weight.
As disclosed in PCT/JP88/989, crystallization is preferably accomplished by either a solvent treatment method or heat crystallization method.
In the solvent treatment method, the prepolymer is crystallized by using a suitable solvent. Examples of suitable solvents include, an aliphatic halogenated hydrocarbon such as chloromethane, methylene chloride, chloroform, carbon tetrachloride, chloroethane, dichloroethane (various isomers), trichloroethane (various isomers), trichloroethylene, and tetrachloroethane (various isomers); an aromatic halogenated hydrocarbon such as chlorobenzene and dichlorobenzene; an ether such as tetrahydrofuran and dioxane; an ester such as methyl acetate and ethyl acetate; a ketone such as acetone, and methyl ethyl ketone; and an aromatic hydrocarbon such as benzene, toluene, and xylene.
Unfortunately the solvent method creates flammability hazzards, results in oligomers, thus requiring an oligomer removal step for acetone recycle. The formed particles can be shattered to a very small size, which can be unacceptable for further polymerization because a typical molecular advancement step utilizes flow of hot nitrogen through a bed of crystallized prepolymer particles. Particles that are too small can then be carried away with nitrogen at moderate nitrogen flow and pressure drop can be excessive due to tight packing of the small particles.
In the heat crystallization method, the prepolymer is heated at a temperature above the glass transition temperature but below the temperature at which the prepolymer begins to melt to crystallize the prepolymer. Crystallization is accomplished simply by maintaining the prepolymer at a specified temperature. As heat crystallization is believed to take too long, there exists a need to reduce the crystallization time.
U.S. Pat. No. 5,204,377, issued Apr. 20, 1993, is directed to a solid-state condensation polymerization process for making polycarbonate. Crystallization is accomplished by a solvent technique in which amorphous prepolymer is treated with solvent under a high shearing force sufficient to reduce the prepolymer to particles having an average particle diameter of 250 microns or less, and a specific surface area of at least 0.2 m.sup.2 /g and a crystallinity of at least 5%, to thereby crystallize and simultaneously render porous the amorphous prepolymer.
JP 5310907, published Nov. 22, 1993, discloses a method of reducing residual organic solvent content by irradiating solvent-containing polycarbonate and/or polycarbonate oligomer with from 300-30,000 MHZ microwave energy.
However, in spite of these advancements in the prior art, none of these prior art references disclose or suggest the application of a water/solvent mixture, or the application of heat crystallization under shear conditions/ to crystallize polycarbonate prepolymer.
Thus, these is still a need for an improved method of making polycarbonate prepolymer.
There is another need in the art for an improved method of making crystallized aromatic polycarbonate.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.